Topic: Feature detection algorithm used by Photosynth?

Just found this excellent steaming video of Blaise talking in-depth about Photosynth. He describes SIFT (Scale Invariant Feature Transform) used in Photo Tourism, but then mentions the Photosynth uses a different, better suited algorithm, but gives no name or details. So, what is it?
TIA.
Reference:
"Cyberspace Arriving - Using Computer Vision to Reconstruct and Connect the World"
Talk by Blaise Agüera y Arcas
Architect, MSN and Virtual Earth
mms://video-jsoe.ucsd.edu/calit2/AguerayArcas.wmv